This invention relates generally to rotary machines, and specifically to turbomachinery. In particular, the invention concerns a shaft speed and vibration sensor apparatus suitable for use with a turbine engine, for example an air cycle machine (ACM).
Turbine engines include turbines, compressors, fans, gas turbines and turbine generators, as well as turbojet, turbofan, turboprop and turboshaft engines for aviation applications. Air cycle machines are a class of turbine engines using a compressor and an expansion turbine to provide refrigeration and cooling by processing a compressible working fluid, usually air. In aviation applications, compressed air is supplied by the bleed system, an auxiliary power unit (APU), or a dedicated compressed air supply.
Air cycle machines are open-cycle systems, in which the working fluid itself is used for primary cooling and ventilation. This contrasts with closed-cycle refrigeration systems, which perform repeated evaporation/condensation cycling of a separate (primary) refrigerant, and then use the primary refrigerant to cool an airflow or water flow, or a process fluid stream.
In aviation applications, the environmental control system (ECS) typically uses one or more air cycle machines to regulate air temperature and pressure in the cabin, cockpit and cargo bay. Each ACM includes a compressor and an expansion turbine, combined with two or more heat exchangers to make up an air conditioning unit or A/C pack. The AC packs cool compressed air in the first heat exchanger, reheat the air in the compressor, then cool the air again in the second heat exchanger before allowing it to expand in the turbine.
The overall pressure ratio from the compressor inlet to the turbine outlet is less than one, so there is sufficient energy in the compressed air supply to drive the ACM compressor via the expansion turbine. Thermal energy is also given up in the heat exchangers, resulting in a cold, relatively low-pressure airflow from the turbine outlet. This flow is mixed with additional (hot) air from the compressed air supply, allowing the environmental control system to regulate internal pressures and temperatures.
To ensure proper operation, the ACM shaft speed must be monitored in order to regulate the compression ratio and exit flow temperature. Over time, air cycle machines and other turbomachinery may also experience vibrations and wobble resulting from bearing damage or shaft deformation, and due to wear and tear on the various rotary components.